Automatic brake mechanism for vehicles



Oct. 29, 1935; G. L. SM|TH AUTOMATIC BRAKE MECHANISM .FOR VEHICLES Filed Dec. 12, 1932 grwc wbob George L. 092221272 Gum/M11 I Patented Oct. 29, 1935 UNITED STATES AUTOMATIC BRAKE DIECHANISM FOR VEHICLES George L. Smith, South Bend, Ind., assignor to United States Ordnance Company, Washington, D. (3., a corporation oi Virginia Application December 12, 1932, Serial No. 646,902

Claims.

My invention relates to automatically adjustable brakes for motor automobiles and airplanes.

The object of my invention is to provide a 8 brake mechanism embodying thermo-controlled means to vary the braking torque and also thermo-controlled means to delay or arrest the adjusting action of the-brake mechanism.

In my Patent 1,792,773 of Feb. 17, 1931, I show 10 mechanism for yieldably anchoring a brake member, the yielding of which causes a reduction in the expanding action of the brake setting means. This yielding movement is accomplished by interconnecting the two anchoring mechanisms of a pair 01' brakes. In my present application I show means whereby the anchoring mechanism of each brake of a motor vehicle or airplane moves independently of the anchoring mechanism of any 26 scribe a structure for controlling the automatic adjustment of a pair of brakes whereby the adjustment of the stronger brake is arrested or delayed until the weaker one'is properly adjusted. This basic idea covered by the aforesaid patent '30 may be accomplished in a variety oi. ways, and one of these ways as described herein embodies a two-arm ratchet lever one arm of which is sov constructed that as it is heated it bends away. from the brake applying lever which actuates 35 it so that its eflective adjusting movement is retarded. t1 In the drawing chosen to'illustrate my inven- Fig. l is an elevation of a right hand brake with brake drum removed, the upper half of brake being cut away to disclose certain parts; Fig. 2, a section on line 2-2 of Fig. 1;

Fig. 3, a section on line 3-3 of Fig. 1 with brak drum outlined; and i 5 Fig. 4, a section on line 4-4 of Fig. 1. The numeral l0 represents the backing plate which carries the brake parts. The anchoring mechanism consists of the pivot stud l I carried by the backing plate, the anchor lever l2 pivoted 50 on H and carrying the abutment l3, the expansion strap 14 of aluminum or some other metal having a high co-efficient of expansion, and the clip l5. As shown in Figs. 3 and 4, strap It lies in the inner angle-of a groove l6 of the backing 55 plate and the end ll thereof is secured to the backing plate by the cap screw l8. The other end of the strap H has a hook l3, (Fig. 2) which engages the outer end of the anchor lever I2 and prevents this lever from rotating in a clockwise direction about the stud II. The clip I5 is riv- 5 eted to the backing plate and also engages the end 20 to prevent the lever 12 from rotating in a counter-clockwise direction.

The brake shoe is .of the duo-servo type con sisting of a primary shoe P and a secondary shoe in S. The webs of these shoes bear against the abutment l3 of the anchoring mechanism when the brake is in released position, being held against it by the release springs 2| and 22. The right hand ends of shoes P and S are connected by an 16 adjustable compression device D consisting of a right and left handed screw 23 with a ratchet wheel 24 at its middle portion and two sleeves 25 which seat in suitable recesses in the ends 26 of the webs. by the springs 21. In Fig. ,1 the sleeve 25 for the shoe P is cut away to show other parts of the mechanism, but .itwill be understood that the appearance of the upper part not shown is the same as the lower part. 26 I A brake expanding device is shown consisting of a lever '28 straddling the abutment l3 and having two lugs 29 and 30 which occupy the gaps 1 between the ends of the webs P and S.; The main part of this lever, as shown in Figure 1, 30 lies just below the web P and has a hook 3| at its upper end to which is hooked the terminal connection 32 of an operating Dull wire 33.

An automatic adjusting lever 34 is provided to adjust the ratchet wheel 24. It is mounted on 36 a pivot 35 secured to the backing plate III at a point substantially in line with the axis of the ratchet wheel and has a short arm 36 and a long arm 37. 'The arm 36 extends between the backing plate and ratchet wheel so ,as to effect 40 engagement with the ratchet teeth of said wheel. A spring pawl 38 secured to the backing plate I0, is bent over onitself to form a support for. the arm 36 and extends beyond it to engage the next tooth of' the ratchet wheelbeyond the one 4 engaged by the arm 36. This permits the centre 39 of the screw 23 to shift a slight amount in a plane parallelv to the backing plate without appreciably affecting the action of the automatic adjustment. This is an important feature of my invention as the screw 23 not only has a certain amount of lateral travel as the brake is applied, but also gradually shifts its position inward as the sleeves 25 travel outon the screw 23. The arm 36 also looks the ratchet wheel from ro-.-

The sleeves are held in these recesses I tating in either direction in a manner similar to that described in my Patent 1,874,131 of Aug. 30, 1932. A torsion spring 40 is mounted on the pivot 35 to operate the ratchet lever in turning the ratchet wheel 24. One end of this spring engages the arm 36 and the other end a pin 4| secured to the backing plate.

The long arm 31 of lever 34 is constructed of two metal strips 42-and 43 of different co-efllcients of expansion and secured together from end to end,- the strip 43 having thegreater coefficient so that the arm will increase its curvature as it heats up and cause the end 44 to bend away from the right edge 45 of lever 28.

The mechanism operates as followsz-The brake is applied by a pull on wire 33 which swings the head 3| of lever 23 to the right and downward. The lever 28 pivots about'the lug 30 and the lug 29 forces the web P away from the abutment l3 and expands the shoes. As the lever 28 swings to the right it presses down on end 44 of ratchet lever 34, rotating it in a counter-clockwise direction. The arm 36 is thus moved away from the ratchet tooth 41 (Fig. 3), and when this movement becomes sufliciently great, due to wear of the brake lining 48, the next tooth to the right will be engaged. When the brake is subsequent- 1y released, the spring 40 will rotate the lever 34 back to its initial position against the stop 49 (Fig. 1) and rotate the ratchet wheel a distance of one tooth.

When the brake heats up due to continued braking the arm 31 will curve away from the edge 45 of the brake lever so that the ratchet lever will not act as soon in picking up a new tooth.

Y Also the strap l4 will increase in length permitting the anchor lever l2 to be rotated clockwise (Fig. 1) a small amount by the normal pressure of the brake against the abutment l3 in the direction of the arrow A. As a result the entire brake shoe with its lever 28 will rotate clock wise (Fig. 1) in proportion to the amount of yielding. of the abutment l3 so that the head 3| of lever 28 will move up and towards the terminal connection 32 of the pull wire 33, in the direction of arrow B. This movement has the effect of reducing the tension in the wire 33 so that the brake pressure drops and the braking action is decreased. The edge 45 of the brake lever also travels up and away from the end 44 of. the ratchet lever so that it will not operate this lever so quickly. Thus the expansion of the strap l4 also acts to retard the action of the adjusting device D. This expansion of the strap due to heat is known to be very small and a strap of considerable length is necessary to provide any appreciable extension. For this reason I utilize a circular member exte;-.d ing around the circumference of the brake and in close proximity to the braking surface of the brake shoe, and while this member is shown positioned in the groove I6 I do not wish to be limited to such a position or to the specific construction of the parts. Broadly speaking I employ a member of large circular form to get as much, length as possible and I position it as close as practicable to the source of heat which is the braking surface of the shoe.

It is thus evident that my brake when con-.

aoraior member which moves in a predetermined direction relative to the other parts of the brake as the temperature of the member and brake parts rises, I wish also to indicate that the expansion strap l4 can be made of metal having a lower 8 co-efllcient of expansion than that of the other brake parts, so that the greater expansion of these parts would produce the same effect as if the strap l4 shortened in length pulling the end l9 down against end 20 and causing the anchor 10 lever l2 to rotate in a counter-clockwise direction (Fig. 1). The resultant rotation of brake shoe and lever 28 will be opposite to the direction of arrows A and B and the tension in pull wire 33 will be increased rather than reduced, thus 15 increasing the brake power. The above arrangement would be usefulon brakes for airplanes as airplane wheels and brakes are usually made of aluminum alloys and the expansion due to heat is extensive, causing considerable foot pedal movement to follow it up. In such a construction the use of a steel strap l4 would reduce this pedal movement considerably and thereby make it possible to increase the pedal leverage and give the pilot an easier brake. This action could not be properly maintained however, without my thermo-controlled ratchet lever to delay the adjusting action of the brake, as in the use of an ordinary type of ratchet lever the movement of the thermo-controlled brake anchorage would act to increase the stroke of such lever, thereby advancing the adjusting action and causing the brake to overadjust itself to the point where it would refuse to release.

The structure shown herein which is responsive to the temperature of the brake to control the adjustment thereof is broadly covered in my copending app ication #562,550 filed September 12, 1931 for Automatic brake adjusting mechanism.

I claim:

1. In a brake, a drum, friction means for engaging the drum, anda movable anchoring mechanism for said friction means including a member having a different co-eflicient of expansion the angular position of the friction means about u I the axis of the drum.

3. In a brake, a drum, friction means for engaging the drum, and an anchoring mechanism for said friction means yielding during brake application to the brake force of the friction means 00 in response to increasing temperature of the brake.

4. In a .brake, a brake drum, friction means for engaging the drum to arrest rotary movement of the latter, and an anchoring mechanism for the friction means movable in response to a change in brake temperature to change the drum arresting action of the friction means.

5. In a brake, a brake drum, friction means for arresting rotary movementof the drum, an automatic adjusting devicefor the friction means, said device including an operating lever responsive to a rise in brake temperature to retard its operative movement, and an anchoring mechanism for the friction means movable in. response to an increase in brake temperature to vary the drum arresting action of the friction means.

6. In a brake, a drum, friction means for engaging the drum, and an automatic adjusting device for the friction means including an operating lever having an arm whose curvature increases with the temperature of the brake.

'7. In a brake, a drum, friction means forengaging the drum, and an extensible device for automatically adjusting the friction means, said device including a ratchet wheel rotatable to extend the device, a movable pawl for operating said wheel, and a fixed pawl supporting said movable pawl and locking said wheel against movement in either direction.

8. In a brake, a drum, friction means for engaging the drum, and an automatic adjusting device for the friction. means to compensate for wear, including an operating pawl a portion of which is constructed of metal strips of different co-efficients of expansion, secured together along substantially their entire length.

9. In a brake, a drum, 2. braking member having a part engageablevwith said drum, and a device for varying the braking action of said braking member,psaid device including a thermo- 10. In a brake, a drum having a 'flange, a backing plate having a groove receiving said flange,

a braking member for exerting a braking torque,

and a device for controlling the torque of said 15 braking member, said device including a thermosensitive element positioned in said groove.

GEORGE L.-SMITH. 

